1. Field of the Invention
This invention relates to threaded connections. More particularly, it relates to the increasing of the torque strength of a threaded connection between a graphite shaft and a metal shaft.
2. Description of the Prior Art
In the refining of aluminum, a rotating nozzle is commonly employed to disperse a refining gas into a body of molten metal contained in a refining vessel. For this purpose, a graphite rotor that thus disperses the refining gas into the molten aluminum is carried on, and is driven by, a graphite shaft. In turn, this graphite shaft is fastened to, and is driven by, a metal shaft, commonly comprising Inconel alloy. These two shafts are fastened together by a threaded connection that must hold the shafts in proper alignment with each other so that they can rotate as one unitary structure. This joint of the two shafts must also transmit the required driving torque from the metal shaft to the graphite shaft. The Pelton patent, U.S. Pat. No. 4,191,486, discloses and illustrates such a threaded connection and the low strengths thereof encountered at elevated temperatures because of the different coefficients of thermal linear expansion of the graphite and metal parts.
In addition to the steady average torque required to drive the rotor in the molten aluminum, additional unsteady shock loads are encountered as a result of changing liquid circulation patterns within the refining vessel and the striking of the rotor by solid objects, undesired but sometimes present in the body of molten metal nevertheless. Such unsteady shock loads can be even greater than, and add to, the normal, steady driving torque referred to above.
The resulting overall torque loads on such threaded connections are high, such as to frequently result in the breaking of the metal graphite joint. This usually occurs by the stripping out of the threads of the graphite shaft. In some instances, however, the graphite shaft becomes cracked in the threaded area thereof. In any event, such failure of the threaded connection is obviously undesired, leading to costly down time, the need for replacement of the graphite shaft, and overall inconvenience and expense in the carrying out of the aluminum refining operation.
It is an object of the invention, therefore, to provide an improved threaded connection between said graphite shaft and the metal shaft employed for the driving thereof.
It is another object of the invention to provide a strengthened threaded connection between a graphite shaft and a metal shaft.
It is another object of the invention to provide a threaded connection between a graphite shaft and a metal shaft having an enhanced ability to transmit driving torque.
It is a further object of the invention to provide a method for the achieving of a joint between threaded graphite and metal shafts having an enhanced ability to transit a driving torque from said metal shaft to said graphite shaft.
With these and other objects in mind, the invention is hereinafter described in detail, the novel features thereof being particularly pointed out in the appended claims.